手写SpringMVC源码-梳理清楚这些你也能手写出来

@Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        String type = req.getParameter(Constant.REQUEST_PARAMETER_TYPE);

        if(type != null && !"".equals(type)){
            if(Constant.SERVLET_TYPE_SAVE.equals(type)){
                // 添加用户信息
                try {
                    saveOrUpdateUser(req, resp);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }else if(Constant.SERVLET_TYPE_UPDATE.equals(type)){
                // 更新用户信息
            }else if(Constant.SERVLET_TYPE_DELETE.equals(type)){
                // 删除用户信息
                deleteUserById(req, resp);
            }else if(Constant.SERVLET_TYPE_QUEYR.equals(type)){
                // 查询用户
                queryUser(req, resp);
            }else if(Constant.SERVLET_TYPE_QUERYBYID.equals(type)){
                // 查询单条记录
                String id = req.getParameter("id");
                User user = userService.queryById(Integer.parseInt(id));
                // 跳转到更新的页面同时保存数据到Request作用域中
                req.setAttribute("user",user);
                req.getRequestDispatcher("/user/userUpdate.jsp").forward(req,resp);
            }else if(Constant.SERVLET_TYPE_CHECK.equals(type)){
                // 验证账号是否存在
                String userName = req.getParameter("userName");
                String s = userService.checkUserName(userName);
                resp.getWriter().println(s);
                resp.flushBuffer();
            }
        }else{
            // 查询用户信息
            queryUser(req, resp);
        }
    }

public interface Controller {

  ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception;
}

public interface View {
  void render(Map model, HttpServletRequest request, HttpServletResponse response);
}

@Override
  public void afterPropertiesSet() throws Exception {
    // 检测@Controller Bean
    for (String beanName : this.applicationContext.getBeanNamesForType(Object.class)) {
      Class beanType = this.applicationContext.getType(beanName);
      if (isHandlerBean(beanType)) {
        detectHandlerMethod(beanType);
      }
    }
  }

/**
   * 初始化 MVC相关组件的策略提供者，从applicationContext中获取
   * 
   * @param applicationContext
   */
  private void initStrategies(ApplicationContext applicationContext) {
    // 1、initHandlerMapping
    initHandlerMappings(applicationContext);

    // 2、initHandlerAdapter
    initHandlerAdapters(applicationContext);

  }

@Override
  protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    // 在这里可把一些Dispatcher持有的对象放入到Request中，以被后续处理过程中可能需要使用到
    req.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE_NAME, webApplicationContext);

    this.doDispatch(req, resp);

  }

private void doDispatch(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    Object handler = null;
    ModelAndView mv = null;
    Exception dispatchException = null;
    try {
      // 1、获取请求对应的handler
      handler = this.getHandler(req);
      // 2、如果没有对应的handler
      if (handler == null) {
        noHandlerFound(req, resp);
        return;
      }
      // 3、如果有对应的handler，获得handler的Adapter

      HandlerAdapter ha = this.getHandlerAdapter(handler);

      // 4、执行adapter
      mv = ha.handle(req, resp, handler);

    } catch (Exception e) {
      dispatchException = e;
    }
    // 5、转发给view
    processDispatchResult(req, resp, handler, mv, dispatchException);
  }

@Override
  public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
      throws Exception {
    // TODO Auto-generated method stub
    RequestMappingInfo mappingInfo = (RequestMappingInfo) handler;
    // ....
    return null;
  }

public interface HandlerInterceptor {
    default boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        return true;
    }

    default void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable ModelAndView modelAndView) throws Exception {
    }

    default void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable Exception ex) throws Exception {
    }
}